This invention relates generally to an electrostatographic printing machine, and more particularly concerns an improved sheet feeding apparatus for use therein.
The art of electrostatographic printing includes both electrographic printing and electrophotographic printing. In both of these processes, an electrostatic latent image, which corresponds to the original document being reproduced, is recorded. Electrophotography achieves this by charging a photoconductive surface to a substantially uniform potential. The charged photoconductive surface is exposed to a light image of the original document. As a consequence of this exposure, the charge is selectively dissipated in the irradiated areas in accordance with the light intensity reaching the photoconductive surface. This creates an electrostatic latent image thereon. Electrographic printing differs from electrophotographic printing only in that the electrostatic latent image is created without the use of photoconductive material. Hence, the process of electrophotographic printing requires the use of a suitable photoconductor whereas electrography does not. The electrostatic latent image created in electrophotography or electrography is developed with a developer mix. Generally, a suitable developer mix comprises colored heat settable plastic particles, known in the art as toner particles mixed with carrier granules, such as ferromagnetic granules. The toner particles and carrier granules are triboelectrically attracted to one another with the toner particles adhering to the outer surface of the carrier granules. As the developer mix contacts the latent image, the greater attractive force of the latent image causes the toner particles to transfer thereto from the carrier granules.
After the toner powder image is formed on the electrostatic latent image, it may be transferred to a sheet of support material. The sheet of support material is frequently advanced from a stack thereof. This is achieved by a sheet feeding apparatus which advances and separates successive sheets from the stack. As the sheet advances, it is aligned to insure that the toner powder is transferred thereto in proper orientation.
Hereinbefore, various techniques were employed to align the advancing sheet. For example, U.S. Pat. No. 3,100,109 issued to Eichorn in 1963 and U.S. Pat. No. 3,199,866 issued to Eichorn et al. in 1965 disclose a sheet of support material forwarded into a paper guide by the action of separator rolls. The sheet of support material is buckled as the separator rolls continue to advance the sheet after the forward motion thereof has been arrested by a gate in the paper path. A paper gripper disposed on a chain advances over the guide and opens the gate. Substantially simultaneously therewith a cam follower on the sheet gripping mechanism opens the individual jaws of the paper gripper so as to receive the sheet heretofore stopped by the registration gate. After the sheet is secured to the paper gripper, the gate then closes exerting a drag force on the sheet of paper being pulled therethrough by the sheet grippers. If the drag is too high, it pulls the paper from the sheet grippers and prevents it from being advanced.
Contrawise, if the gate force is too light, a sheet of substantially stiff paper will push the gate open without being aligned. Thus, the force exerted by the registration gate must be optimumly designed in view of the fact that the drag must be minimal while the sheet is advancing therepast. However, the force in the closed position must be sufficient to prevent a stiff sheet of paper from moving the registration gate out of position prior to the alignment thereof. The foregoing contradictory requirements are difficult to achieve in a sheet feeding apparatus and, frequently, when not attained, result in paper jams and sheet misfeeds within the electrophotographic printing machine. This results in excessive machine downtime and increased maintenance costs.
Accordingly, it is a primary object of the present invention to improve the sheet feeding apparatus by achieving a more efficient registration system therefor.